Detection of a common feature in several human tumor cell lines--a 53,000-dalton protein

Human cell lines, whether derived from spontaneous tumors or transformed in vitro with simian virus 40, were found to contain a 53,000-dalton phosphoprotein (pp53) in contrast to normal human cells in which this protein was not detected. Isoelectric focusing showed that pp53 comprised several species in both simian virus 40-transformed and tumor cells. Comparison of the pp53 species from the various cell lines by partial proteolysis showed that they were similar but not identical. Among the 13 tumor cell lines examined, only 1 line, HeLa, did not contain detectable pp53. All the other tumor cell lines contained pp53, and it is suggested that this protein may be associated with their transformed state.